We are studying the effect of tumor necrosis factor (TNF) on MCF-7 human breast cancer cell growth and metabolism. We found that TNF inhibits growth of these cells in a dose-dependent manner. TNF acts by arresting growth in the GOG(1) phase of the cell cycle. We also found that TNF completely blocks estradiol stimulation of growth. This is dose-dependent for TNF, and growth is blocked for all concentrations of estradiol. TNF down regulates the estrogen receptor in dose-dependent manner as demonstrated by both Scatchard analysis and EIA; this occurs without a change in the receptor affinity constant (KD). Down-regulation is blocked by cycloheximide and thus TNF requires continuous protein synthesis for this effect. TNF significantly increases resting levels of the progesterone receptor (PgR) in dose-dependent manner. This effect is also blocked by cycloheximide. The increase in PgR levels in these cells is not accompanied by altered growth response to exogenous progestins. TNF, however, does not block estradiol stimulation of progesterone receptor synthesis, and does not block estradiol down-regulation of the ER. We also found that, in contrast to its effects on cells in the immune system, TNF does not act synergistically with IL-1 to inhibit growth of these human breast cancer cells. This is true for varying doses of either IL-1 and TNF. IL-1 transiently enhances TNF mRNA expression at 3 hours; this is not associated with increased secretion of TNF, and therefore TNF does not appear to mediate the inhibitory of IL-1. In contrast, TNF persistently enchanced TNF MRNA in these cells, beginning at 3 hours and lasting unchanged through at least 72 hours of exposure. This is associated with increased secretion of TNF into the media; TNF may therefore act in an autocrine manner on these cells to inhibit cell growth. IL-1 and TNF do not act synergistically to alter TNF MRNA expression. We are currently studying the effect of TNF on growth and metabolism of MCF-7 cells in vivo, the effect of TNF on gene expression of ER and PgR MRNA, the effect of TNF on expression and secretion of the growth factors TGF-beta and IGF and on EGF receptor expression, and modulation of these proteins by estradiol.